a) Field of the Invention
The present method relates to a method and a portable testing apparatus for safely testing an autotransformer for power distribution lines.
b) Background of the Invention
Known in the art, there is the U.S. Pat. No. 2,910,646 of E. J. Schutzner, granted on Oct. 27, 1959, wherein there is described a portable ratio tester for transformers. This portable ratio tester comprises a carrying case, a source of low voltage pulsations, and a four arm bridge circuit having resistances in arms three and four in the same ratio as the anticipated ratio of the transformer windings to be connected. The tester also comprises binding post terminals on its case for connecting the primary winding of the transformer into arm one of the bridge circuit, and for connecting the secondary winding of the transformer into arm two of the bridge circuit, a galvanometer bridged across the bridge circuit from a point between arms one and two to a point between arms three arid four, and means for applying the voltage pulsations upon the terminals in arm two for the transformer secondary winding. In operation, when the transformer windings are properly connected in the bridge circuit, the voltage applied across the bridge circuit will be the sum of the applied voltage plus the voltage induced in the transformer primary winding.
Also known in the art, there is the U.S. Pat. No. 4,654,806 of T. D. Poyser et al., granted on Mar. 31, 1987, wherein there is described a method and an apparatus for monitoring transformers. This method comprises steps of monitoring at least one parameter related to transformer load, collecting periodic load data in response to the monitored parameters, monitoring transformer parameters related to transformer condition, collecting periodic data in response to the monitored parameters related to transformer condition, establishing predetermined load threshold values, establishing predetermined condition threshold values, comparing said periodic data with said predetermined load threshold values, comparing said periodic condition data with said predetermined condition threshold values, and evaluating transformer performance in response to the comparison steps.
Furthermore, there is the U.S. Pat. No. 4,772,978 of Yoshifumi Oura et al., granted on Sep. 20, 1988, wherein there is described a transformer protection system. In this transformer protection system, data of voltages and currents detected at individual terminals of a transformer connected to an electric power system are supplied to a computer. The computer computes driving point admittances or shunt admittances of the transformer on the basis of the voltage and current data and predetermined transfer admittances of the transformer and decides that an internal fault has occurred in the transformer when the values of the driving point admittances or shunt admittances deviate from pre-set reference values, thereby disconnecting the transformer from the electric power system.
The patents described hereinbefore, do not provide a method having necessary steps by which a user can safely test an autotransformer of power distribution lines, and they do not provide a portable testing apparatus having necessary means for safely testing the autotransformer.
Also known in the art, there are the U.S. Pat. Nos. 2,527,568; 2,657,356; 2,911,591; 3,231,817; 3,678,429; 3,742,346; 3,769,576; 3,823,369; 4,241,306; 4,362,987; 4,758,774; 4,857,827; 4,857,856; 5,034,681 and 5,172,067, describing different transformer monitoring systems and methods, and testers for windings in transformers or other electrical components. But none of these patents describe a method having necessary steps by which a user can safely test an autotransformer of power distribution lines and a portable testing apparatus having necessary means for safely testing the same.